You should be able to demonstrate that you have good control of your disease, HBA1c. Get an insulin pump and continuous glucose monitor. There are NYPD cop's with type 1 diabetes on patrol and one I know after 911 went to a pump it made things much easier. There is even a new one called Omni Pod with no tubes to deal with. You can set your pump to silence.
Problems for combat where you might be on a long deployment or taken prisoner, just keeping insulin cool could be an issue. If you would be willing to take an administrative post so that you could finish your four year enlistment maybe this is possible.
Try to enlist the aid of your local congressmen, have your family contact him or her. There are amputees that are being alowed to continue their enlistment. Type 1 is an autoimune disease with no known cause, you did not bring this upon yourself by eating to much, type 2 is a disease of metabolism that can sometimes be helped by diet.
If you are interested their are several police agencies that do not consider Juvenille diabetes to be a barrier to being hired and the experience that you have already would be greatly valued.
Good luck.
I don't know if this will help you... but there was another concersation posted in this forum at
http://www.medhelp.org/forums/Diabetes/messages/130.html. If they yank the URL - search here under "Military Discrimination". It has a lot of information from all walks of life.
And good luck to you!!!